The present invention relates to anion laser tube and, particularly, to discharge portion of a high power ion laser tube.
In an ion laser tube which generates laser oscillation by utilizing transition between energy levels of ionized gas such as argon or krypton, etc., it is required generally that ion density is increased with increase of output power thereof. In order to achieve this requirement, it is general to flow large current exceeding 20 amperes through a discharge portion. Therefore, the discharge portion has to be made of material having high heat conductivity, so that heat generated in the discharge portion can be efficiently radiated, and durability against plasma of high ion density. An example of such material which has been used widely is crystalline graphite in view of its heat durability and easiness of treatment.
Since, however, graphite product is usually porous, it is easily sputtered by high ion density plasma, resulting in dust as well as gas emission.
In order to measure these defects, it has been proposed to coat the discharge portion of graphite with molybdenum by using thermal spray technology. An example of this technique is disclosed in Japanese Utility Model Application Laid open No. Sho 58-39064.
However, for many reasons, such as that thermal expansion coefficient of graphite is different from that of molybdenum and adhesion of a molybdenum layer prepared by thermal spray to the graphite base member is relatively low, such molybdenum coating is easily peeled off when the discharge portion is subjected to high temperature due to discharge of a working laser tube and sputtering, etc., and the molybdenum layer peeled off may clog an optical path of the laser tube. Further, a large amount of gas may be emitted from a portion of the graphite member exposed from the molybdenum layer. Such gas discharge may shorten the life of the ion laser tube and may cause an initial operational failure thereof. Further, dust of the molybdenum layer peeled off from the graphite member may deposit on opposite optical windows of the ion laser tube during transportation thereof, which may cause a long distance transportation of the ion laser tube to be impossible.